Hi guys. I just want to know why at the point "A" there is 10 volts and not 12 volts witch is the sum of the two power supplies in series. Thanks!.

 

Point A to what other point?

 

You should consider what the term 'in series' means with regard to connecting the power supplies, and how that is represented in your diagram.

 

A voltage is measured between two points, a current flows between two points. Presumably the 10V and 2V mean the voltage between the positive and negative terminals of the respective batteries. Though I do have some sympathy for students who are asked to analyze meaningless circuits.

 

A voltage is measured between two points, a current flows between two points. Presumably the 10V and 2V mean the voltage between the positive and negative terminals of the respective batteries. Though I do have some sympathy for students who are asked to analyze meaningless circuits.

Analyzing meaningless problems is the basis for all education. If you can understand the stupid, it's easier to understand the logical.

 

Unless it is stated otherwise, the voltage reference for a point in a circuit is usually circuit common or ground. In that case, the voltage between point A and ground is the voltage across the terminals of the 10V source.

 

Unless it is stated otherwise, the voltage reference for a point in a circuit is usually circuit common or ground. In that case, the voltage between point A and ground is the voltage across the terminals of the 10V source.

What i don't understand is why the 12v is distributed between the 2 resistors but at the point A there is 10v. I mean if at that point we've got 10v then why these 10volts aren't distributed between the to resistors instead of the 12v?. In my mind i think that in that point should be 12v so that this tension could drop on the two resistors.

 

Can you state the actual question that has been put to you?
There are quite a few voltages you can measure, depending what the question is.
Maybe you can mark on the circuit what voltage is across each part and that you can work any voltages out.

 

There is never a voltage at a point.

It is like asking, what is the distance at Madrid?
We can agree there is no valid answer. We can ask, what is the distance from Barcelona to Madrid?

Similarly, we can ask, what is the voltage with respect to common?
What is the voltage at point A with respect to common? +10V.
What is the voltage at point B with respect to common? -2V
What is the voltage at point A with respect to point B?
The answer is +10V - (-2V) = +12V.

 

Hi guys. I just want to know why at the point "A" there is 10 volts and not 12 volts witch is the sum of the two power supplies in series. Thanks!.

As others have said, voltage is always a difference in potential energy (per unit charge) between two points.

Whenever we talk about the voltage AT a point, the inference is that it is the voltage between that point and some agreed upon common reference point. In your diagram, the chassis ground symbol is identifying that reference point (and it's not the proper symbol to use, but everyone knowns what was meant).

Think of a height analogy. Start at the ground symbol and think of that as actual ground level. Then the 10 V battery is like building a platform ten feet tall and Point A is the top of that platform. Point B is reached by digging a two foot hole in the ground. The two resistors are on a string connecting Point A to Point B. The difference in height between A and B is 12 ft, but A is 10 ft above the ground and B is 2 ft below the ground.

 

In this example, V1 is assumed to be a perfect voltage source with zero resistance, thus the voltage at Point A to ground cannot be anything other then the voltage of V1.

 

As others have said, voltage is always a difference in potential energy (per unit charge) between two points.

Whenever we talk about the voltage AT a point, the inference is that it is the voltage between that point and some agreed upon common reference point. In your diagram, the chassis ground symbol is identifying that reference point (and it's not the proper symbol to use, but everyone knowns what was meant).

Think of a height analogy. Start at the ground symbol and think of that as actual ground level. Then the 10 V battery is like building a platform ten feet tall and Point A is the top of that platform. Point B is reached by digging a two foot hole in the ground. The two resistors are on a string connecting Point A to Point B. The difference in height between A and B is 12 ft, but A is 10 ft above the ground and B is 2 ft below the ground.

Perfect. Thank you. Your analogy was the key.

 

Hi guys. I just want to know why at the point "A" there is 10 volts and not 12 volts witch is the sum of the two power supplies in series. Thanks!.

View attachment 285249

V1 and V2 are NOT in series- they have a ground between them. so V2 is grounded on both sides. Get this, it will help-

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3

 

V1 and V2 are NOT in series- they have a ground between them. so V2 is grounded on both sides. Get this, it will help-

Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3

How is V2 grounded on both sides?

Since there is no other connection to ground in this circuit, the ground symbol only serves to identify the common reference node. V1 and V2 are in series unless and until something else is connected to this ground.

 

How is V2 grounded on both sides?

Since there is no other connection to ground in this circuit, the ground symbol only serves to identify the common reference node. V1 and V2 are in series unless and until something else is connected to this ground.

V2 is grounded on the positive side, and it's on ground polarity is on the other side (in other words, neither side of V2 can contribute to adding voltage to the circuit.



Based on how the battery symbol is drawn for V2, the bottom is (+), and the top is (-). Which matches a series relationship to the other battery (V1). But the Earth Ground a the bottom is the problem.

 

V2 is grounded on the positive side, and it's on ground polarity is on the other side (in other words, neither side of V2 can contribute to adding voltage to the circuit.

View attachment 285639

Based on how the battery symbol is drawn for V2, the bottom is (+), and the top is (-). Which matches a series relationship to the other battery (V1). But the Earth Ground a the bottom is the problem.

How are you getting that "it's on ground polarity on the other side"? The negative terminal of the batter is connected to Node B. So?

Whatever current flows through the 2 V source must flow through the 10 V source. It can't flow out through the ground connection because there is no path for it to get back to either source. This, by definition, places the two elements in series.

As soon as any other path is created to this ground, THEN they would no long be in series.

ANY node in a circuit can be declared to be the reference node and doing so has no effect on the circuit.